Dielectric Properties Of Flake Magnesium Oxide-Based Filler/Polyvinylidene Fluoride Composites

Polymer-based composite dielectric materials play a key role in advanced electronic devices and power systems.At present,extensive research has been carried out to improve the dielectric properties of the materials.But achieving low losses and good reliability is still a great challenge.Inorganic nanosheets materials have great potential for applications in solving these problems because they possess unique structure and properties.However,the properties of the materials such as low dielectric constant,easy agglomeration and surface inertness have become the obstacles to their applications.Designing structures for filler by introducing other materials with different properties can solve effectively the above problems.In this paper,polydopamine(PDA)and short carbon nanotubes(SCNT)were successively loaded on the surface of self-made magnesium oxide(Mg O)nanosheets.The preparation technologies of two types of the novel composite filler,as well as the effect of their structure on the dielectric properties of polyvinylidene fluoride(PVDF)-based composite films were studied.Firstly,on the surface of round Mg O nanosheets with a diameter in the 200～300nm range and a thickness of about 16 nm prepared by hydrothermal calcination method,PDA like worms loaded by in-situ polymerization.The composite filler is almost stacking-free and uniform in size when the mass ratio of Mg O to DOPA is 25:1.Dielectric constant of the Mg O-PDA/PVDF composites with 2 wt%filler loading undergoes a decrease with increasing frequency.Nevertheless,the values are significantly higher than those of the Mg O/PVDF composite and pure PVDF film in the range of less than 10~6 Hz.At 10~3 Hz,the dielectric constant is 10.91,which beats them by 1.75 and 2.80,respectively.The dielectric loss of the composite decreases and then increases with the various frequency.The values are below 0.1 within the frequency of 3×10~3～10~6 Hz,and a minimum value of 0.04 occurs at 10~5 Hz.The enhancement of the dielectric constant can be attributed to the interface polarization of PDA and the increasing conversion rate of theβ-phase of PVDF.The suppression of dielectric loss is attributed to the fact that Mg O nanosheets can obstruct the free charge movement.Based on the above work,the Mg O-PDA/SCNT composite filler with hierarchical structure was designed and prepared by adjusting the mass ratio of Mg O-PDA to SCNT.When the mass ratio was 15:1 and 20:1,the SCNT loading content was high and the size of the products is uniform.At 10~3 Hz,the dielectric constants of the two types of the Mg O-PDA/SCNT/PVDF composites(2 wt%)are 13.97 and 14.62,which are more than 3.06 and 3.71 higher than that of the Mg O-PDA/PVDF composite.The values of dielectric loss are higher by 0.04 and 0.13,respectively.However,the dielectric loss can be suppressed within about 0.05 range near 10~4 Hz.Moreover,the dielectric loss exhibits an increasing trend with the increase of SCNT loading content.Conductive SCNT loaded on the surface of Mg O-PDA filler can improve the dielectric constant because of the local electric field homogenization inside the composite,and also raise the leakage loss due to the charge carrier.